A main wing made of aluminum alloys used in aircraft is composed of separately manufactured outer plates, beams, and ribs, and the wing is assembled by fastening these parts with rivets. However, when the abovementioned parts are fastened with rivets, there is an unavoidable increase in the number of assembly processes due to rivet hole forming work and rivet driving work, a concentration of stress in the rivet holes, and a drop in the smoothness of the wing surface at the rivet head parts.
Accordingly, a method in which the main wing is joined by welding has been proposed in U.S. Pat. No. 6,116,539 as a method for solving such problems. This main wing is shown in FIG. 12 hereof.
Referring to FIG. 12, the aircraft forward wing structure 100 comprises a wing upper surface box structure 101, a wing lower surface box structure 102, and an intermediate spar 103. The wing upper surface box structure 101, wing lower surface box structure 102, and an intermediate spar 103 are respectively joined by laser welding. As a result, the problem of rivet fastening is solved.
Since the abovementioned laser welding is performed on materials made of an aluminum alloy, welding defects such as solidification cracks, blow holes, and the like are generated in the welded parts, and there is a danger that the mechanical strength in the welded parts will drop.